Direction responsive means



July 31, 1934.' H D, TEAR I 1,968,542

DIRECTION RE SPONS IVE MEANS Filed Sept. 22. 1930 2 sheets-sheet 1 Fig. I.

"umuwwim Fig.2. A

Z/B 65 Inventor /A James D. Tear fig by My? M H'Ls Attorney July 31, 1934.

J. D. TEAR 1,968,542

DIRECTION RESPONSIVE MEANS Filed Sept. 22, 1930 2 Sheets-Sheet 30 Kg'f/POSCOPI C eff''ci' D0 FL 6.

y/resu/tant eff'ct (E V E 90 60 70 @[60 0 N E 5 W v vertical component effect v 83 94 --gyro(.gcwz aplc effect v 7. resu/Zfant effect Inventor James D, Tearbg Hts Attorney.

Patented July 31,

1,968,542 nmsc'rron RESPONSIVE MEANS James D. Tear, Schenectady, N. General Electric Company, a

New York Y., assignor to corporation of Application September 22, 1930; Serial No. 483,735

22 Claims. (o1. 33'-204) My invention relates to directionresponsivemeans, .more particularly to such means provided with a pendulously stabilized element, and has for its object the provision of an accurate and reliable direction System and automatic steering system having special (application to airplanes, and the like.

It will be understood that compasses of the type responsive to the direction of the earth's l0 magnetic field, such as magnetic and electromagnetic compasses, have the common characteristic of an element stabilized in a horizontal plane, usually by means of an inertia or pendulous device. For land or water craft such com-- .15 passes are entirely satisfactory. For airplane operation, however, the environment for the compass is quite different, involving among other things turns at relatively high angular velocity about a center of curvature remote from the airplane. Such turns produce centrifugal forces which throw the pendulous device outward along the radius of turn curvature thereby displacing the stabilized element of the compass in proportion to the speed and angular velocity. This displacement brings the stabilized element into the influence of the vertical component of the earths magnetic fleld with. the

,- result that the compass is caused to give erroneous indications.

Because of this turn error, it is practically impossible with compasses heretofore-used to hold a predetermined course by following the compass indication alone, the pilot being compelled to supplement the compassby reference to the horizon, land marks, or when flying blind to a gyroscopictum indicator, It is an'object -of my invention, therefore, to provide in one instrument all of the advantages of both the 4 compass-and the gyroscopic turniniiicator, to-

gether with other advantages, whereby by following one indicating element the pilot can readily maintain a predetermined course.

Obviously, no error is introduced in the compass when-the turn .is made substantially about the center-of gravity of the airplane, since no centrifugal forces are then set up to displace invention has application to compasses ofthe electromagnetic type having an elongated stabilized element, such as alined pole pieces, for concentrating and intensifying the effect of theearths magnetic fleld, as described and to claimed in my Patent No. 1,863,421, dated June 14, 1932. This compass is most commonly used with the pole pieces set at right angles with the earth's field when the airplane is on the v desired course, the compass indicator operating 5 as a zero reader. With the plane flying in a northerly or southerly direction a turn tilts the poles from their horizontal position into the influence of the vertical component of the, earths fleld and an error is thereby introduced. 79 For northerly courses the practical effect of this error is to cause the compass to give deceptive indications and thereby tend to cause oversteering with a resultantirregular course. For southerly courses the turneffect is reversed and is such as to introduce noambiguity into the compass indications, but to actually assist in maintaining a straight course. For due east and west courses, the turn effect is such as-to introduce-no angular error.

In carrying out my invention -in one form I provide means responsive to the angular 'veloc--- ity of the airplane for introducing a modifying function in the operation-of the compass, so as to overcome the detrimental effects of the turn error. My invention also coniprehen'ds an automatic steering system embodying this angular velocity responsive function.

For a more completeunderstanding of my invention, reference should be had to the accomo panying drawings in which Fig. 1 is a fragmentary view showing a compass system for airplanes embodying my invention; Fig. 2 is a diagrammatic view illustrating certain features of operation of the system, Figs. ,3 and 4 are fragmen tary diagrammatic views showing modified forms 0 my invention, Fig. 5 is a fragmentary view I showings still further modification of my invention, Figs. 6 and '7 are curves showing the various functions involved, Fig. 8 is a fragmentary dia- '100 grammatic view showing an automatic steering system embodying my invention, while Fig. 9 is a fragmentary view partly in section showing the claimed in my Patent No. 1,863,421, although it will be understood that my invention is' not limited to this particular type of compass as one element of the system. The poles 11 and 12 are secured in alignment with each other on a horizontal frame 13 which is provided with supporting pivots 14 and 15, mou'nted in hearings in a vertical supporting framelfi. The frame 16 is provided with a short supporting spindle l'Lat its upper end which is mounted in a bearing provided for it on a horizontal supporting member or plate 18, forming a part of the structure of the plane or rigidly secured to the plane. Mounted for rotation between the inner enlarged ends of the pole pieces 11 and 12 is a spherical armature 19 provided with hearings in the upper and lower sides of the frame 16. The shaft 20 of the armature extends through the spindle 1'? so as to project above the plate 18 for connection with suitable driving means (not shown), such as a wind motor. The pole pieces and the magnetic core of the armature are made of a suitable magnetic material having high permeability and low retentivity, such as an alloy of 78 /2% nickel and 21 iron. The supporting structure for the pole pieces and the armature or various parts of it are made of a suitable non-magnetic material such as an aluminum alloy in order to avoid any magnetic shielding effect from these parts or a magnetic short circuit between the pole pieces.

Suitable brushes 21 and 22 cooperate as'shown with a commutator connected to the winding on the armature 19. These brushes are electrically connected respectively to collector rings 23 and 24 which are secured to the frame 16 in insulated relation with each other and with the frame. By means of suitable brushes (not shown) cooperating with the rings 23 and 24, and conductors 25 and 26 leading from the brushes, the rectified output of the armature is applied to the voltage coil 2'7 of a galvanometer indicating instrument 28 provided with a pointer 29. The sensitivity of the instrument can be varied by adjusting a variable resistance 2'7 connected across the coil 27.

The spindle support 1'7 of the instrument provides for adjustment of the pole pieces in a horizontal plane whereby the desired course may be set. As shown, a worm wheel 30 is secured to the upper end of the frame 16, while a worm 21 secured to the plate 18 cooperates with the worm wheel so that by turning the worm by means of the crank 32 connected to it through a flexible chain or cable 33 the position of the frame 16 and hence of the poles 11 and 12 may be adjusted as desired in a horizontal plane. A suitable device is provided for stabilizing the pole pieces 11 and 12 about their pivot axis defined by supports 14 and 15 so that the pole pieces normally lie in a horizontal plane. This stabilizing means is shown as a pendulum 34, in the form of a vane, moving in a sector-shaped casing 35 containing oil whereby a suitable dampingaction is applied to the movement of the pendulum.

It will be understood that the pivot axis of the pole pieces 11 and 12 intersects their center line at right angles thereto and further that the axis of rotation of the armature 19 passes through this point of intersection at right angles to the center line of the pole pieces and their pivot axis. The instrument is so supported on the plate 18 by means of the spindle support 17 that the axis of rotation of the armature is normallyvertical, i. e., when the airplane is flying on.an even keel and on a level course. With the airplane flying on the desired course the pole pieces are positioned with their center line transverse to the horizontal component of the earths field, and hence no magnetic flux is induced in them and no voltage is generated in the armature. The pointer.29 is then in the central zero position shown in the drawings.

For a northerly or southerly course, the pole pieces are set at some angle with the fore and aft line of the airplane. If now under these conditions the airplane is turned with a bank, for example, to correct the course, it will be obvious that the pendulum is swung outward in a radial direction with respect to the axis of the turn in response to the centrifugal forces whereby the pole pieces are tilted from the horizontal, the inner pole piece moving downward. The amount of this tilt varies with the cruising speed of the airplane, the rate of turn and as the cosine of the angle of course setting measured from north. In this tilted position the pole pieces are influenced by the vertical component of the earths field. For northerly courses the effect of the vertical component for such a corrective turn is in the same direction as the positional effect due to the horizontal component, and consequently increases the displacement of the pointer 29 from the central position, tending to mislead the pilot.

When the airplane arrives back on its course the positional effect due to the horizontal component is zero, but the pointer will still be displaced by the effect of the vertical component and indicates a further corrective turn. As the airplane swings to the opposite side of its course, assuming that the pilot is steering in response to his indicator, the ellect of the horizontal component increases from zero in the opposite direction and opposes the effect of the vertical component. Eventually it will be equal to the eifect of the vertical component and bring the pointer to zero. The airplane, however, will then be on the opposite side of its course. This predominating effect of the vertical component in producing an erroneous indication persists for an interval of time dependent upon the course setting and the cruising speed of the airplane. The duration of this time interval is quite appreciable, being 14 seconds for an airplane traveling in a north course at I00 miles per hour. Considerable judgment is therefore required of the pilot in order to hold a straight course.

For southerly courses the effect of the vertical component is reversed, since the opposite pole piece is then tilted downward by the turn, and tends to bring the pointer back to the central position more quickly. In other words, the indicator is made more sensitive to the corrective steering.

Now for small rates of turn, the effect of the vertical component is proportional to in which V the cruising speed of the airplane, W angular velocity of the turn, and g acceleration of gravity. In accordance with my invention I provide means responsive to the angular velocity of the turning movement, shown as a gyroscope 36, for generating a control magplied with current from a suitable battery 38 through conductors ,39 and-40 whereby an armature element 41 forming the rotor is caused .to-

' rotate. This. armature element 41 is mounted is introduced in "the circuit of the indicating instrument 28 so as to oppose the vertical com--" on suitable bearings on the stationary supporting shaft 42 of the field member. The shaft 42 I 'is rigidly secured" at .its ends'to' the frame 43 which is provided with pivot supporting pins 44 and 45 mounted in hearings in the supporting pedestals 46'and 47, the axis of the pivot pins be n perpendicular to the axis of rotation got the rotor 41.

The axis of the pivot pins 44 and 45 is the precession axisof the gyroscope; The pivot pin 45 carrieson its outer end a contact arm 48 cooperating with a resistance49, the contact arm being electrically insulated from the pin 45. Under normal conditions, that is, with no precession the frame 43 is centered in a mid-position by a spring 50 so that, the contact arm 48 I is in engagementwith the middle of the resistly across the battery. 38, as is also the resistance;

51. A central tap on the resistance 51 is con- 'nected' by a conductor 52, a resistance 53, and a conductor 54 to the contact-arm48 whereby a ance 49. The resistance 49 is connected direct potentiometer bridge arrangement is formed.

' With the contact arm 48 in a central position as 7 shown, no voltage is applied to the resistance 53, but movement of the arm in either'direction applies a voltage to the resistance varying with the amount of the movement and depending in polarity upon the direction of the movement.

, This resistance 53 is includedin the circuit of the conductor 26 between the electromagnetic compass 10 and the indicating instrument 28, an adjustable connection 55 being. provided whereby the amount of voltage drop included in the circuit can be adjusted as desired. The polarity of the battery 38 and the direction of precession of the gyroscope, and hence movement of the contact arm 48, are so selected that for northerlycourses the voltage drop across the resistance 53-will be in opposition-to the voltage induced in the armature 19 by the vertical component of the earths field. The velocity of rotation of the gyroscope about its spin axis is so selectedand the connection 55 is so adjusted that for all practical cruising speeds the voltage drop introduced in the instrument circuit by the resistance 53 is greater than the voltage in the armature due to the vertical component. 56 and 57, preferably made of an elastic mate- .rial, are provided to limitthe precession of the .associated with the crank. This adjustment may be made at any time and the pilot will bring the airplane to the desired course by watching his indicator. The steering technique, however, is no ,longer that of the compass but that of the turn indicator. ,The operator is instructed to keep Stops the pointer on or near its central position. For purposes of illustration, assume that the airplane is flying along a course west of north, as indicated by'the dotted line X, of Fig. 2. Assuming that the pole pieces 11 and 12 are adjusted for that course they will be in some such position as indicated at A. Assume now that a setting is made for due north, then the 'pole pieces will be turned to the position indicated at B. The operator in response to his indicator, which preferably is connected sothat for a right hand deviation its pointer moves to the left of the central position, now banks for a right hand turn following a course somewhat as indicated by the dotted line Y. This tends to introduce a turn error in the voltage output of the electromagnetic compass 10, as previously explained, but the voltage produced bythe precession of the gyroscope in response to the angular velocity of the turn is greater. Consequently the indicator is graduallybrought back toward the central zero position until the algebraic sum of the two turn eiiects, that due to the gyroscope and that due to the vertical component of the earth's field, be-

comes equal to the positional eflect given by the horizontal component'of the earths'field when the indicator will be on zero. The indicatorordinarily will reach this central zero position in an early stage of the turn and in response thereto the operator begins tostraighten out the airplane. g A

As the turn proceeds-the positional effect may become less than the turn effect, and the indicator pointer 29 will then move to the opposite or right hand side of the zero position. Upon ob-;

serving this the operator still further straightens out the airplane as indicated by the dotted line Y of Fig. 2. As he proceeds to do this keeping the pointer on or near the central position, the angular velocity of the airplane decreases and is thus automatically kept proportional to the angular distance from the set course. Consequently the airplane arrives on its course with its angular velocity practically zero so that no over steering results. It is therefore very easy for the pilot to maintain a predetermined course or to change to a new course.

Departure of the airplane from the set course ordinarily will take place with an angular-veloc's course.

It will be understood that the action of the yarious elements of the system is the same but in the opposite sense wherethe deviation from the desired course is toward the right instead of toward the left, as assumed in the example just given. For courses in a southerly direction, the gyroscopic control means is not. absolutely necessary since in this case the turn error is reversed and tends to bring the pointer back more quickly to its central-position and consequently there is no danger of over steering. As will be described in connection with Fig. 3, it may be desirable to provide means for automatically decreasing the effect of the gyroscopic control as the course deviates from the north.

In the preferred .form of my invention shown in Fig.- 3, I have shown a carbon pile resistor 60 in place of the resistance 49, theresistance of v the carbon pile being varied by means of an arm 61 which corresponds with the arm 48 of Fig. 1. This arrangement has the advantage that the 'actual precessional movement of the gyroscope is very small and in fact is hardly appreciable so that the axis of rotation of the gyroscope is not displaced by precessional movement as is true of the arrangement of Fig. 1. The arrangement of Fig. 1 has the disadvantage that where this displacement or tilting of the axis of rotation occurs so as to bring the axis out of a horizontal plane, angular movement of the airplane about its athwart axis may cause the gyroscope to precess. In other words, the gyroscope may then be responsive to pitching, which of course introduces errors in the indicator. With the carbon pile arrangement of Fig. 3, however, the axis of rotation of the gyroscope remains parallel to the transverse axis of the airplane, the precessional force, which is proportional to the angular velocity, being utilized without appreciable movement to control the resistances in the legs of the potentiometer.

As shown the carbon resistance 60 is divided into two sections with the contact arm between them. Preferably a small clearance is provided for the contact arm. Various other elements of Fig. 2 will be understood from the previous descriptions in connection with Fig. 1, a battery 62 being provided as a source of potential across which the resistance 60 is connected in parallel with the resistance 63. The contact arm 61 and the midpoint of the resistance 63 are connected respectively by conductors 64 and 65 to the terminals of the resistance 66, which corresponds to the resistance 53 of Fig. 1.

In Fig. 3, however, I have also shown a preferred arrangement whereby the gyroscope output is automatically and gradually controlled as the course setting deviates from north. This means comprises a circular potentiometer resistance 67 cooperating with which is a contact arm 68 mounted on the worm wheel 69corresponding with the worm wheel 30 of Fig. 1 by means of which the compass is set for the desired course. Cooperating with this worm wheel is the worm 70 which is turned to make the setting. When the airplane is headed on a magnetic north course, i. e. parallel with the direction of the earths magnetic field, the contact arm 68 is in the position indicated with respect to the potentiometer and makes direct contact with the conductor 64 leading to the contact arm 61. The connection from the contact arm leadsthrough a conductor ring 71, a cooperating brush 72, conductor 73, and switch arm 75 to one end of the resistance 66. An-electrical connection 74 is also provided between the conductor 65 and a point on the potentiometer resistance 67 exactly opposite the "connection therewith for the conductor 64.

In the operation of this arrangement when the worm wheel69 is turned to introduce a course setting deviating from the magnetic north, the contact arm 68 moves with it in one direction or the other depending upon whether the setting is for west or east of north and as a result introduces a certain amount of the resistance 6'7 in the circuit. This gradually decreases the effect of the gyroscope as the course diverges from the north, since the voltage drop in the potentiometer resistance 67 is subtracted from the total drop in voltage between the conductors 64 and 65 so that there is a smaller voltage drop across the resistance 66. For southerly courses the contact arm 68 points downward, and for a due south course the contact arm makes contact with the point 74 which it will be observed short circuits the resistance 66 and consequently entirely cuts out the gyroscope.

In the southern hemisphere, it is to be noted that the effect of the vertical component of the earths field is reversed and consequently the resistance 67 of Fig. 3 should then be connected for an opposite effect so as to gradually decrease the gyroscopic efl'ect as the course deviates from due south. Furthermore, in the equatorial region the vertical component of the earths field is small and consequently when flying in such regions it is desirable that the gyroscopic effect should be independent of course setting.

I have, therefore, provided a second contact arm 68 on the worm gear 69 in a position 180 degrees displaced from the arm 68. This arm 66 is connected by a contact ring and a brush to a switch contact 75* whereby by throwing the switch arm 75 upward into engagement with this contact the system may be changed for flying in the southern hemisphere.

Furthermore, the conductor 64 is continued through a resistance 64 to the switch contact 75 so that by moving the switch arm 75 upward into engagement with this contact, the gyrois desirable for flying in the. equatorial regions.

This reduced effect of the gyroscope is preferably of some such value as indicated by the resultant curve 9 of Fig. 7.

It may be desirable to have substantially exact compensation for the vertical component for all courses and in all latitudes. This substantially exact compensation can be obtained, as shown in Fig.4, by driving the gyroscope at a speed proportional to the cruising speed of the airplane and by varying the voltage output of the gyroscope in accordance with the cosine of the course setting angle 0 measured from north and the sine of the angle of dip D, i. e;, the inclination of the earths magnetic field to the horizontal, and furthermore by suitably adjusting the constants of both the electromagnetic compass and the gyroscope. The constants can be most conveniently proportioned by varying certain constants of the gyroscope, such as the base speed of the gyroscope, the tension of the spring 50, and the setting of the movable contact 55 on the resistance 53.

It will be obvious that for complete compensation the voltage Ew introduced into the compass or indicating instrument circuit by the gyroscope must be equal and opposite to the voltage Ev introduced into the compass circuit by the vertical component of the earths magnetic field. In other words for complete compensation H=total earths magnetic field. =angle of bank of the airplane.

0=course setting angle, measured from north. q

D=angle of dip, i. e., inclination of H to the horizontal.

The problem now is to introduce suitable functions into the voltage Ew introduced into the come pass circuit by the gyroscope so as to make this voltage "equal to the above calculated value of.

Ev under all conditions. The course setting angle 0 can be easily obtained from the course setting mechanism and'the angle of dip D is known. Therefore, by means of suitable potentiometers the variables cos 0 and sin D can be introduced into the total voltage output Eg of the gyroscop so that we may write (2) Ew==E cos 6 sin D But by calculation in which b==constant of gyroscope device.

=angular velocityof gyroscope about its spin axis. v

g=gravitational acceleration. 1 v=linear cruising speed of airplane.

Substituting for Eg in Equation (2) (3) E =bg sin qt cos 0 sin D It will be observed that this last value of E1! has only two variables which do not appear in Equation. 1 for Ev, i. e., the angular velocity 0 of the gyroscope about its spin axis and the cruising speed o. By driving the gyroscope about its spin axis at a speed proportional to the cruising speed, as by a wind motor or by connecting the driving motor of the gyroscopeto a wind driven generator, the speed of the gyroscope becomes substantially equal to some constant k times the cruising speed and we may write the equation Substituting for n in Equation (3) Ew=bkg sin cos 0 sin D Therefore, it will be observed from the above equation that it is now necessary only to adjust the constants of the electromagnetic compass and the gyroscopic device so that and substantiallyexact compensation will be ob'- tained under all cruising conditions.

This substantially exact compensation is given by the apparatus shown in Fig. 4. It will be understood that the conductors 64 and 65 in this Ill) figure correspond with the similarly numbered conductors in Fig. 3 and have applied to them the The conductors 64 and 65 (Fig. 4) lead to a I resistance potentiometer '77 which is circular in form and has aligned contact arms .17 and '77 which are mounted in insulated relation with each other so as to be driven by the course setting mechanism in the same manner as arms of the potentiometer 6'1 of Fig. 3. The resistance of this potentiometer is so arranged that it is varied and the voltage across the contact arms '77? and 77 likewise varies with the cosine of their angular displacement that is the cosine of the course setting angle 0 measured from north. For

a n'orth course setting the contact'arms are in a vertical position as shown in the drawings with the contact arm 77- in direct contact with the conductor 64 and the contact arm '77 in contact with the conductor 65. The course setting angle is then zero so that the cosine of the angle is one and consequently E; under these conditions is not varied by the potentiometer 77. For a due cast or west course the contact arms are displaced 90 in one direction or the other from the north position, depending upon the direction of course, to a mid-position in which case cosine 0 equals zero and no voltage is applied to the contact arms. For "southerly courses involving a displacement'from the north position of more'than 90 it will be apparent that the voltage applied to the contact arms is reversed to compensate for the reversed efiect of the vertical component.

The voltage from the contact arms 7'7 and 77 is applied by meansof suitable slip rings, brushes and conductors '78 and 78 to a second circular potentiometer 79 provided with alined contact arms 79 and '79 which are adjusted manually in accordance with the angle of dip D measured from the horizontal equatorial position. When flying atthe north magnetic pole the-contact 'arm '79 is set in a contact atthe point N while when flying at the south magnetic pole the contact arm '79 is setdn contact with the point S. The resistance ofthis potentiometer is arranged to vary in proportion to the sine of angle of adjustment of its contact arms and thereforevary as sine D, i. e. the angular displacement of the brushes from the horizontal position. This potentiometer thus introduces the function sine D into the voltage Eg. It will be observed that for flying at the equator with the dip angle equal to zero, and hence sin D equals zero, no voltage is impressed on the conductors 80 and 81,.while the function sin D is reversed for flying in the southemhemisphere; For the north pole setting the contact arms '79"- and '79 are connected directly withthe conductors 78 and 78 and since full voltage is applied to the contact arms, the dip angle then being 90, whence sin D==1. For the south pole setting the voltage is reversed.

the voltage,across the contact arms 79 and 79 This voltage across the contact arms is applied by means of suitable slip rings brushes and conductors 80 and 81 to a resistance 82 which corresponds with the resistance 53 of Fig. 1, a portion or all of this resistance being included in the indicating instrument circuit.

In the arrangement shown in Fig. 5, a direct mechanical connection is provided between the ,gyroscope and the poles 11 and 12-of the compass, which are stabilizedby the pendulum 34. With this arrangement the gyroscope precesses so -as to tilt the poles during a turn and thus introduces an eifect proportional to' rate of turn. This effect is added algebraically to the other effects exactly as described earlier in connection with Fig. 1.

In the arrangement shown, the frame 83 of the gyroscope is mounted on the depending arms 83 and 83 secured to the main frame 84 of the compass. This mounting is alsosuch that the. axis of rotation of the gyroscope is maintained parallel with the center line of the poles 11 and 12*. One of the prccessional pivot supports of the gyroscope carries an arm 85 havmg a iorked frame 89 carrying the pole pieces 1'1 and 12. It will be observed that the turning movement of the airplane causes the gyroscope to precessand turn the arm 85 in one direction or the other depending upon the direction of the turning movement and thus tilt the poles 11 and 12.

The direction of rotation of the gyroscope is suchthat for northerly courses the precession, of

the gyroscope during a turn tilts the poles in a.

direction opposite to the tilting tendency of the pendulum 34 and by an amount greater than the tilting tendency of the pendulum. In other words,.the pole pieces are given an opposite inclination whereby the compass turn. effect is rely the two effects are cumulative. The net result is therefore the same as with the system of Fig. l, the compass indicator being made more sensitive to corrective steering for all courses. rangement of Fig. 5 can be applied to a magnetic compass, the needle being pivotally mounted on and constrained to-rotate in the place of frame 89.

A clear and accurate understanding of the turn error, the function of the gyroscope in Figs. 1 to 3 and the result obtained may perhaps be facilitated by reference to the graphic illustrations given in Figs. 6 and '7. The curves shown in these figures are plotted against the angles of the course setting as abscissa and gyroscope and vertical component eiiects in terms of voltage as ordinates. The abscissa starts with north at zero, with east 90 degrees therefrom and continuing to south, west and back to north at 360 degrees. The voltages are taken for some predetermined constant cruising speed and angular turning velocity of the airplane. It .will be observed that the gyroscopic' effect for Figs. 1 and 5 as shown by the dotted line 90 (Fig. 6) has-a -Thelalgebraic sum of these two effects, shown by the sinusoidal curve 92, is positivefor all points of the compass since thegyroscopic effect is the greater.

It will be understood that this resultant effect, curve 92, is opposedduring aporrective turn to the positional effect of the horizontal component. Consequently, when theairplane is turned toward the set course at the proper rate, the

algebraic sum of the vertical component effect and the gyroscopic effect become equal to the positional effect and the indicator reads zero. As

previously explained after this condition obtains the pilot steers to maintain the indicator on zero.

Fig. 7 shows the condition existing with the preferred form shown in Fig. 3. In this case the gyroscopic eifect varies due to the influence of the potentiometer resistance 67 of Fig; 3, being maximum with a due north setting and varying as a straight line function to zero with a due The ar south setting. Curve 94 shows the sum of this gyroscopic effect and the vertical component effect of curve 91", Fig. 6. This curve can be made quite flat, indicating a resultant turn effect which is quite constant for all course settings. It will be understood that when flying in the southern hemisphere the curve 91 is inverted, and the curve 93 can likewise be inverted by moving-the contact arm 75 into engagement with the con- The relation of the various voltages may be indicated mathematically as follows: plane is so maneuvered that the pointer is held on zero the following relation exists.

Eh-l-(Ev-I-Ew) =0 in which Es=voltage due to horizontal component of earths field.

'Ev=voltage due to vertical component curve 91 of Fig. 6.

' -Ew=voltage proportional to angular velocity derived from the gyroscope (curve Fig. 6, curve 93 Fig. 7). r

These relations hold true for Figs. 1, 3 and 5 of my invention.

In the form of my invention shown in Fig. 3 with the resultant effect (Ev+Ew) approximately a straight line (curve 94 of Fig. 7), this resultant effect becomes approximately proportional to the angular velocity and consequently we may write for small rates of turn, the equation- Eo+Ew=KW in which K=a constant W=angular velocity of the turn Substituting in the first equation we have Eh+1fW0 Solving for W Therefore W varies as Eh.

' In other words, with the pilot steering to hold the indicator on the central zero position with the form of my invention shown in Fig. 3, the angular When the v Nil velocity at which .the airplane approaches the set course is proportional to the angular distance from the desired course, and becomes zero as the course is reached.

The exact relation between the angular velocity called for by the compass system to bring the pointer to zero for a given departure angle A0 from a set course may be expressed by the following two equations:.

W=g/v tan 0 Mil 01100 miles per hour calls for a rate of current associated with an angle of bank of'approximately 19 degrees to bring the pointer to zero. This;

angle of bank will be gradually decreased-as the course is approached. It will be seen that for small angles of bank these equations lead to the approximate equations previously discussed.

In Fig. 8 I have shown the application of my invention to automatic steering whereby a straight line course is held; It is contemplated that the apparatus shown diagrammatically in Fig. 8 will controls two vacuum tubes 99 and 100 which in turn control the clutch magnet coils 101 and 102. These magnet coils control the connection and disconnection of a continuously operating electric motor 103 with the driving mechanism 104 for the rudder. j

In order to introduce a follow up movement .the rudder is provided with a contact arm 105 which cooperates with aresistance 106 connected in parallel with a similar resistance 107 tothe filament supply source for the tubes, shown as a battery 108. Cooperating with the resistance 107 is a contact arm 109 which is electrically connected to the contact arm 110 of the polarized relay. Incidentally, as .shownfthis contact arm 109 isalso electrically connected to the coil circuit of the relay. It will furthermore be observedthat with these connections the contact arm 109 is connected to the coil circuit at a point between the coiland the resistance 9'7. The contact arm 105 is connected by a conductor 111 to the terminal of the resistance 97 opposite theterminal to which the contact arm 109 is connected.

,Inthe operation of the system the grids of the tubes are given a sufllciently negative bias by the battery 112 and high resistances 113, 114 so that thetubes do not normally pass current. Upon .deviation from the course, however, the member 110 of the relay moves either to the right or to the left depending upon the direction of the deviation and makes an electrical contact with one or the other of the grids of the tubes through a relatively low resistance 115 or 116 This supplies sufilcient positive bias from the filament battery 108 through theresistance 107 to produce operation of the tube and thereby energize the clutch coil 101 or 102. The rudder is thus connected to the motor and is turned by, the motor in the appropriatedirection. At the same time the contact arm 105 is moved over the resistance 106 and voltage therebyapplied to 'the resistance 9'1. It will be understood that the contact arm 109 is preferably set in a mid-position on the resistance 107. Thegpotential drop across the posite thereto, the rudder will hav'ebee'n given a setting corresponding to the amount of devia-.. tion of the airplane-from the course. .At this time thevoltage supplied to the relay 96 will of f coursebe zero and its contact arm will return 'Fig.1.'

to its control biased position shown on the drawings, interrupting the grid circuit to the tube! and deenergizing the magnet coil whereby the motor 103 is disconnected from the rudder.

As the airplane returns to its course, the voltage across the conductors 25 and 26 decreases as will be understood from the previous description in connection with Fig.1. e potential drop in the resistance-9'Lthen predominates and the con-' tact arm 110 of the relay is thrown in the opposite direction to produce operation of the other tube whereby the motor 103 is connected to the rudder so as to turn it back toward its central position.. The tendency of the automatic control is therefore to'maintain-a-zero voltage acrossthe conductors 25 andl26, and consequently the air-'- plane is brought on the course at an angular rate varying with the angular distance from the course whereby the conditions fulfilled by the pilot in manual steering are duplicated.

In Fig. 9I'have shownthe details of the electromagnetic clutch between the motor 103 and the rudder 117. The motor drives a bevelled gear 118 which meshes'with two' bevel gears 119 and 120 loosely mounted on the drive shaft 121. The gears 119 and 120 are of course continuously driven in opposite directions by the motor. The

gear 119 is provided with a cylindrical extension 122 which forms part of the magnetic flux path for the magnet winding 101. The magnet winding is preferably stationary and mounted on a magnetic member 123, also forming part of the flux path, which encircles the shaft 121, A copper ring 124 is built into the gear 119 sqas to interrupt the flux path through the gear, it being completed through the complementary. clutch member 125 which is splined on the shaft 121. When the coil 101 is energized the clutch member 125 is pulled over into engagement with the inner face of the gear 119 whereby \the drive shaft 121 is connected to the gear 119 for rotation of the rudder in one direction. It will be understood that the arrangement of the gear 120 and the magnet coil 102 is the same as previously described in connection with the gear 119 and the coil 101.

The various parts of the clutch are enclosed in' a supporting casing 126.

' It will be understood that the automatic helm controlling mechanism may also be appliedto the systems of Figs. 3,4 and 5 by connectingjhe control relay to the indicating instrument circult in the manner described in connection with While I have shown a particular embodiment of my invention, it will be understood, of course,

that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claimsto cover any such modifications as fall within the true spirit-and scope of my invention. i

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is: i

l. The combination in a direction system for airplanes and the like, of means for generating a voltage varying in value and direction in dependence upon the angular relation of the airplane with relation to the earths field, an indicating device responsive to said voltage, a -revoltage or'isaid resistance inoppositionto the voltage produced by said generating means whereby said indicating device is responsive to the algebraic sum of said voltages.

2. The combination in a direction indicating system for airplanes and the like, of a compass provided with pole pieces, pendulous means for stabilizing said poles pieces in a horizontal plane,

voltage generating means responsive to the ma netic flux induced in said pole pieces by the earths magnetic field, an indicating device responsive to said voltage, a resistance in the circuit of said indicating device, gyroscopic means .for producing a second voltage in dependence upon the angular turning velocity of the airplane and connections whereby said voltage is impressed on said resistance in opposition to the voltage produced by said generating means. 3. The combination in a direction system for airplanes, and the like of a compass provided with pole pieces, pendulous means for stabilizingpole pieces, pendulous means for stabilizing said pole pieces, voltage-generating means responsive to the flux induced in said pole pieces by the earths magnetic field, direction-indicating means connected to said voltage-generating means, means responsive to turning movement of the airplane for modifying the operation of said indicating means, means for angularly adjusting said pole pieces for a desired course, means for varying said modifying action in accordance with the sine of the angle through which said pole I pieces are adjusted, and an operating connection between said course adjusting means and said last mentioned means.-

5. The combination in a direction system for airplanes or the like, of means provided with pendulously stabilized pole pieces for generating a voltage in dependence upon the magnetic flux induced in said pole pieces by'the earths field, an indicating device responsive to said voltage, a resistance in the circuit of said indicating device, gyroscopic means for regulating a second voltage having a magnitude dependent upon the angular turning velocity of the airplane and a polarity dependent upon the direction of said turning movement, said voltage being {of greater magnitude than the component of said first voltage produced by the vertical component of the earths field, connections whereby said second voltage is impressed upon said resistance, a second variable resistance connected with the first resistance, means for varying the said second resistance, course setting means for adjusting said pole pieces to introduce the desired course setting and an operating connection between said course setting means and'said resistance varying means arranged to gradually. vary said second resistance from a maximum value for a predetermined course to zero for another course whereby the voltage applied to said first resistance is correspondingly varied.

6, The combination in a direction system for airplanes and the like, of means provided with pendulously stabilized pole pieces for generating a voltage in dependence upon the fiux induced in said pole pieces by the earths field, an indicating device responsive to said voltage, gyroscopic means for regulating a second voltage so that it has a magnitude dependent upon angular turning velocity of the airplane, and a polarity dependent upon the direction of said turning movement, said voltage being of greater magnitude than the component of said first voltage produced by the vertical component of the earth's field, a resistance electrically connected to said gyroscopic means, means for varying said resistance so as to vary said second voltage in accordance with a cosine function, course set ting means for adjusting said pole pieces to introduce a desired course setting angle, and operating connection between said course setting means and said resistance varying means, a second resistance connected to said gyroscopic means, means for varying said second resistance in accordance with a sine function, and means for introducing the resultant voltage derived from said second resistance into the circuit of said indicating device.

7. The combination in a direction system for airplanes and the like, of a compass provided with pole pieces, pendulous means for stabilizing said pole pieces in a horizontal plane, voltagegenerating means responsive to the magnetic flux induced in said pole pieces by the earths magnetic field, gyroscopic means for regulating a voltage in dependence upon the angular turning velocity of the airplane, indicating means responsive to the algebraic sum of said voltages, a resistance connected to said gyroscopic means,

means for varying said, resistance, course setting means for adjusting said pole pieces for a pre-- maximum for a predetermined course to zero for another course.

8. The combination in a direction system for airplanes and the like, of a compass provided with pole pieces, pendulous means for stabilizing said pole pieces in a horizontal plane, voltage-generating means responsive to the magnetic flux induced in said pole pieces by the earths magnetic field, an indicating device responsive to said voltage, a resistance in the circuit of said indicating device, gyroscopic means for regulating a second voltage so that it has a magnitude dependent upon the angular turning velocity of the airplane and a polarity dependent upon the direction of such turning movement, said voltage being of greater magnitude than the component of said first voltage produced by the vertical component of the earths field due to displacement of said pendulous means upon turning movement of the airplane, connections whereby said second voltage is impressed upon said resistance, a second variable resistance connected in parallel with the first resistance, means for varying said second resistance, course setting means for adjusting said pole pieces to introduce a desired course setting and an operating connection between said course setting means and said resistance varying means arranged to gradually 45 9. The combination in a turn responsive system for airplanes and the like, of a compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass is normally responsive to the horizontal component of the earths magnetic field whereby said compass has an inherent turn error dependent upon the angular velocity of the airplane in making a turn, turn indicating means for said compass, and gyroscopic means responsive to the angular velocity of the turning movement of said airplane for operating said indicating means jointly with said compass so as to introduce a corrective magnitude in said indicator having a predetermined relation to said turn error.

10. The combination in a turn-indicating system for airplanes and the like, 0! an electromagnetic compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass normally generates a voltage varying in value and direction in accordance with its angular relation with the horizontal component of the earths field, a voltage-responsive turn-indicating instrument connected to said compass, means responsive to the angular turning velocity of said airplane about an axis remote therefrom for regulating a second voltage so that it is substantially greater than the voltage induced in said compass by the vertical component of the earths field due to displacement of said compass about said horizontal axis by centrifugal iorces incident to said tuming movement, and connections for applying said second voltage to said tum-indicating instrument in opposition to the voltage of said compass when said airplane is flying on a northerly course.

11. The combination in a direction system for airplanes and the like, of a generator arranged to be excited from the earths magnetic field provided with an armature and a magnetic pole piece mounted for pivotal movement about a normally horizontal axis, pendulous means for stabilizing said pole piece about said horizontal axis so that said pole piece directs into said armature the magnetic flux induced in said pole piece by the horizontal component of the earths magnetic field, a voltage-responsive turn-indicating instrument connected to said generator, angular velocity responsive means responsive to turning movement of the airplane about a vertical axis remote therefrom for regulating a second voltage so that it is substantially greater than the voltage induced in said generator by the vertical component oi. the earths field due to displacement of said pole piece about said horizontal axis by centrifugal forces incident to such turning movement, and connections for applying said second voltage to said tum-indicating instrument in opposition to said first voltage when said airplane is flying on a northerly course.

12. A compass system for airplanes and the like comprising an electromagnetic compass for generating a voltage varying in value and direction in dependence upon the angular position of said airplane with relation to the earth's mag netic field, said compass being provided with pendulous stabilizing means whereby said compass is normally responsive to the horizontal component of the earths field, means responsive to the angular velocity of the airplane in making a turn about a vertical axis remote therefrom for regulating a second voltage so that it has a predetermined relation to the voltage induced in said compass by the vertical component of the earths field due to displacement of said compass by centritugal i'orces incident to such turning movement, course-setting means mounting said compass for adjustment about a normally vertical axis until said voltage is zero when the airplane is moving on a predetermined course, means operated by said course-setting means Ior regulating said second voltage, and indicating means responsive to the algebraic sum of said voltages.

13. The combination in a direction system for airplanes and the like, of electromagnetic compass means for generating a voltage varying in value and direction in dependence upon the angular position of the airplane with relation to the earths field, said compass being provided with pendulous means for stabilizing it about a normally horizontal axis, voltage regulating means, angular velocity responsive means for operating said voltage regulating means to regulate a second voltage so that it is substantially greater than the voltage induced in said compass by the vertical component of the earths field due to displacement of said compass about said horizontal axis by centrifugal forces inci dent to such turning movement, indicating means responsive to the difference in said voltages, a resistance connected to said voltage regulating means, means for varying said resistance to vary the effect of said voltage regulating means, course-setting means movably mounting said compass for adjustment about a normally vertical axis to bring said indicating means to a predetermined position when the airplane is directed on a predetermined course, and an operating connection between said resistance-varying means and said course-setting means whereby the effect of said regulating meansis varied in accordance with the course setting.

14. The combination in a direction system for airplanes and the like, of electromagnetic compass means for generating a voltage varying in value and direction in dependence upon the angular position of the airplane with relation to the earth's field, said compass being provided with pendulous means for stabilizing it about a normally horizontal axis, angular velocity responsive means for regulating a second voltage so that it is substantially greater than the voltage inducedin said compass by the vertical component of the earths field due to displacement of said compass about said horizontal axis by centrifugal forces incident to such turning movement, indicating means responsive to the difference in said voltages, course-setting means movably mounting said compass for adjustment about a normally 'vertical axis to bring said indicating means to a predetermined position when the airplane is directed on a predetermined course, auxiliary means for regulating said second voltage, and a driving connection between said auxiliary means and said course-setting means for operating said auxiliary means in proportion to the cosine of the course angle.

.15. The combination in a direction system for airplanes and the like, of an electromagnetic compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass normally generates a voltage varying in value and direction in accordance with its angular relation with the horizontal component of the earths field, said compass having a voltage induced therein by the vertical component of the earths field due to displacement of said compass about said horizontal axis by centrifugal forces incident to turn ing movement of the airplane about a remote vertical axis, a gyroscope for regulating a second voltage in proportion to the angular velocity of said turning movement of the airplane, means for driving said gyroscope at a speed proportional to the cruising speed of the airplane, means for varying said second voltage in accordance with the cosine of the angle of flight, means for varying said second voltage in accordance with the sine of the angle of dip whereby said second voltage is made equal and opposite to said vertical component voltage under all conditions, and indicating means differentially responsive to the voltage of said compass and said second voltage.

16. A compass system for airplanes and the like, comprising an electromagnetic compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass normally generates a voltage varying in value and direction in accordance with its angular relation with the horizontal component of the earths field, course-setting means mounting said compass for adjustment about a normally vertical axis until said voltage is zero when the airplane is moving on a predetermined course, means responsive to the angular turning velocity of said airplane about a vertical remote therefrom for regulating a second voltage so that it is substantially greater than the voltage induced in said compass by the vertical component of the earths field due to displacement of said compass about said horizontal axis by centrifugal forces incident to such turning movement, auxiliary means connected to be driven by said course-setting device for varying said second voltage, means for reversing the effect of said auxiliary voltage-varying means, and indicating means differentially responsive to said voltages.

17. A compass system for airplanes and the like, comprising an electromagnetic compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass normally generates a voltage varying in value and direction in accordance with its angular relation with the horizontal component of .the earth's field, course-setting means mounting said compass for adjustment about a normally vertical axis until said voltage is zero when the airplane is moving on a predetermined course, means responsive to the angular turning velocity of said airplane about a vertical axis remote therefrom for regulating a second voltage so that it is substantially greater than the voltage induced in said compass by the vertical component of the earth's field due to displacement of said compass about said horizontal axis by centrifugal forces incident to such turning movement, indicating means diiferentially responsive to said voltages, a resistance connected to control said indicating means, means for varying said resistance to independently control said indicating means, an operating connection between said course-setting means and said resistance-varying means, and means for reversing the connections between said resistance and said indicating means.

18. The combination with a compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass is normally responsive to the horizontal component of the earths magnetic field, indicating means operated by said compass, means responsive to the angular velocity of turning movement of said compass about a vertical axis remote neeacae' therefrom, and a driving connection between said angular velocity-responsive means and said compass tending to tilt said compass about said horizontal axis in a d rection opposite to the tilting eifect of said pendulous stabilizing means due to centrifugal forces incident to turning movement about a vertical axis remote from said compass.

19. The combination with a compass provided with pendulous means for stabilizing said cornpass about a normally horizontal axis so that said compass is normally responsive to the horizontal component of the earths magnetic field, of indicating means operated by said compass, auxiliary means for operating said indicating means independently of said compass, and means responsive to the angular velocity of turning movement of said compass about a vertical axis remote therefrom for operating said auxiliary means so as to overcome the effect of the vertical component of the earths field on said compass due to displacement of said compass about said horizontal axis by centrifugal forces incident to said turning movement.

20. The combination in a turn-indicating system for airplanes and the like, of a compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass is normally responsive to the horizontal component of the earth's magnetic field, turn-indicating means operated by said compass in accordance with the deviation of the airplane from a predetermined course, auxiliary means for operating said indicating means independently of said compass, and means responsive to the angular velocity of turning movement of said airplane about a vertical axis remote from said body for operating said auxiliary means so as to tend to move said indicating device in a direction opposite to its movement by said compass by an amount substantially greater than the effect of the vertical component of the earths field due to displacement of said compass about said horizontal axis by centrifugal forces incident to such turning movement.

21. The combination in a turn-indicating system for airplanes and the like, of an electromagnetic compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass normally generates a voltage varying in value and direction in accordance with its angular relation with. the horizontal component of the earths field, a voltage-responsive turn-indicating instrument connected to said compass, means responsive to the speed of the airplane for producing a second voltage varying in accordance with the speed of the airplane, means responsive to the angu-= lar turning velocity of said airplane about a vertical axis remote therefrom for regulating said second voltage so that it is substantially greater than the voltage induced in said compass by the vertical component of the earths field 'due to displacement of said compass about said horizontal axis by centrifugal forces incident to such turning movement, and connections for applying said second voltage to said turn-indicating instrument in opposition to the voltage of said compass when said airplane is flying on a northerly course.

22. A system for steering an airplane or the like along a predetermined course, comprising an electr -magnetic compass provided with pendulous means for stabilizing said compass about a normally horizontal axis so that said compass normally generates a voltage varying in value and direction in accordance with its angular relation with the horizontal component of the earth's field whereby saidcompass has a voltage induced in it by the vertical component of the earths field due to displacement of said compass about said horizontal axis by centrifugal forces incident to turning movement about a vertical axis remote therefrom, means responsive to the 

